There are many models on the runway who have naturally curly hair especially on the finer side. On top of that they get keratin treatments which straightens, shines and de-frizzes hair. If we had to make a generalization about the hair type on the runway it would be fine and not thick hair. For example, Patricia van der Vliet and Lindsey Wixson both have naturally very curly hair but they get hair treatments. Many models also get their hair blown out and extend the days between washes. So no, the models casted for shows are not necessarily more towards the straight hair side.